For legacy queues the only call of blkg_root_lookup() happens after
bypass mode has been enabled. Since blkg_lookup() returns NULL for
queues in bypass mode, modify the blkg_root_lookup() such that it
no longer depends on bypass mode. Rename the function into
blk_queue_root_blkg() as suggested by Tejun.
Suggested-by: NTejun Heo <tj@kernel.org>
Fixes: 6bad9b21 ("blkcg: Introduce blkg_root_lookup()")
Signed-off-by: NBart Van Assche <bart.vanassche@wdc.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>